I have a question not regarding a Heathrow-Gatwick transfer but a LHR-LHR 'transfer.'

I am flying in on AA. Great, I can bring two bags at 70 lbs. each. However, my connection to NBO is the next day on a separate reservation.

According to BA.com I am down to 51 lbs.! So I loose 89 lbs. just like that. Great.

Is there any way to have my two flights put under the same PNR or record locater or something so that I can have more of a chance of being allowed to bring two bags over 51 lbs.?

Thanks for any advice or personal experiences.